1. Field of the Invention
The present invention relates to a method, a terminal, and a system for establishing a Push to Talk Over Cellular (PoC) group session in a PoC system. More particularly, the present invention relates to a method, a terminal, and a system for providing an Invitation Reservation Service (IRS) while interworking with a PoC eXtensible markup language Document Management Server (XDMS).
2. Description of the Related Art
As a result of breakthroughs in mobile communication technology and extensive use of communication networks, a larger range of services and applications are provided via mobile telephones. In addition to basic communication services, users are demanding more diversified services, including a positioning service, a multimedia service, and a Push to Talk (PTT) service. In particular, the PTT service supports various additional functions (e.g., instant messenger, condition indicator, etc.), as well as group and voice communication provided by conventional wireless telegraphs or Trunked Radio Systems (TRSs).
Various efforts are being made in the industry to realize the concept of PTT as a service based on mobile communication networks, i.e. PoC service, and enact corresponding standards. One of the distinctions between conventional mobile communication services and the PoC service is that, according to the latter, users can perform communication while moving between sessions, if necessary, because they belong to a plurality of sessions. The requirement that users must be able to communicate while moving through a plurality of sessions is described in PoC Regulation 1.0 of Open Mobile Alliance (OMA), an organization regulating pertinent mobile communication services.
The PoC Regulation 1.0 provides that a PoC session is divided into a one-to-one PoC session and a group PoC session. Such a PoC session is initiated when a PoC client transmits a session request message to a PoC server. However, when all members of an ad hoc group session or prearranged group session want to participate in communication, the session initiator must confirm one by one if all clients can communicate at that time. To this end, the PoC client must repeatedly subscribe to and check the presence information of corresponding clients. Such repeated check of presence information requires signaling via wireless access networks. This increases the cost and wastes wireless resources.
In an attempt to solve this problem, it has been suggested to employ a Session Initiation Protocol (SIP) PUBLISH method to realize network-based session initialization. According to this conventional technique, a PoC terminal requests a PoC service to provide an IRS, and session setup parameters are stored in the PoC server in response to the request. As used herein, the IRS refers to a service, the session of which is initiated from a network by presence information or other session setup parameters.
The technique requires extension of the format of an eXtensible Markup Language (XML) schema for a PoC service setting, as provided by PoC Regulation 1.0, and XML data is stored in the PoC server. Considering the characteristics of XML data, which requires dynamic access to stored documents and convenience in editing, storage of IRS data in the PoC server may increase the load on the server during management of PoC sessions, e.g. when a number of PoC group sessions are established.